The present invention relates to composite injection mouldable material and in particular to platable injection mouldable material having a relatively high dielectric constant and low dielectric loss.
Applications such as RF (Radio Frequency) applications require devices having a high dielectric constant and a low dielectric loss. It is known to use metallised ceramic components for these applications, produced using established technology to cast and fire the ceramic. However, the machining of these components is generally difficult and only simple planar structures are possible. Metallisation to form interconnection and tracking is also a specialist activity and the resulting components tend to be heavy.
Composites of polytetrafluoroethylene (PTFE) and ceramic have found increasing use in similar applications. The composite is more easily machined and patterned than ceramics. However, it is may only be made in sheet form.
In accordance with a first aspect of the invention an injection mouldable material comprises a composite of an injection-mouldable polymer and a ceramic filler.
Preferably the loss tangent of the polymer is equal or less than 0.010 (which corresponds to a Q of 100) and greater than or equal to 0.002 (which corresponds to a Q of 500) at 1 GHz. Preferably these characteristics are maintained for frequencies up to 2.5 GHz.
In accordance with a second aspect of the invention an injection mouldable material comprises a composite of an injection-mouldable polymer and a filler having a dielectric constant of at least 9.
Thus the invention enables the production of devices requiring a high dielectric constant and low loss, which are light and capable of being injection moulded. Complex 3D structures may be constructed which may be plated, preferably using Moulded Interconnection Device (MID) technology.
The filler is chosen to have a high dielectric constant compared with the polymer and low dielectric loss. A dielectric constant in the range of 9-250 is contemplated for the filler.
The material has a relatively high dielectric constant which allows a reduction in the physical size of RF devices such as antennas. This has particular application to internal antennas where market forces are demanding ever smaller devices. In addition a material having a high dielectric constant allows better control of field patterns, thus making devices more directional and efficient. The low dissipation factors of the material also minimise the energy loss in the device structure and hence maximise the energy radiated.
Preferably the polymer is polyetherimide and the filler is a ceramic. Another particularly suitable polymer is SPS (synthiotactic polystyrene). These polymers are chosen for their good plate-ability characteristics.
The filler may have a dielectric constant of at least 9.8, preferably at least 30 or 100. Preferably the filler is Titanium, Baxe2x80x94Ti or Alumina.
Advantageously the filler may comprise at least 10% by weight of the material and preferably at least 30% to 60% by weight of the material. Clearly the higher the percentage of the filler, the higher the dielectric constant of the composite material will be. The amount of filler which may be used is generally limited by the mechanical properties of the resulting material e.g. polyetherimide with more than 60% Titania may become too brittle or not suitable for injection moulding.
Devices formed of a material according to the invention are thus lighter than prior known devices formed from ceramic and may be formed into complex structures. The material is particularly suitable for the manufacture of antennas although it is suitable for many other high frequency applications.
In a further aspect of the invention, a method of manufacturing a composite material comprises mixing a ceramic substance with an injection-mouldable polymer, heating the mixture and extruding the composite material.
Preferably the ceramic substance is in a powdered form and the polymer is in a granulated form.
In a yet further aspect of the invention, a method of manufacturing a device comprises injection moulding material comprising a composite of an injection-mouldable polymer and a ceramic substance to form the device.
In a yet further aspect of the invention there is provided an antenna formed from a material comprising an injection mouldable polymer and a ceramic substance. Such an antenna is particularly suitable for use with portable communication devices, for example radio telephones, etc.